Fluorescence in situ hybridization (FISH) is a powerful technology wherein nucleic acids are targeted by fluorescently labeled probes and then visualized via microscopy. FISH is a single-cell assay, making it especially powerful for the detection of rare events that might be otherwise lost in mixed or asynchronous populations of cells. In addition, because FISH is applied to fixed cell or tissue samples, it can reveal the positioning of chromosomes relative to nuclear, cytoplasmic, and even tissue structures, especially when applied in conjunction with immunofluorescent targeting of cellular components. FISH can also be used to visualize RNA, making it possible for researchers to simultaneously assess gene expression, chromosome position, and protein localization.
Labeled probes in FISH methods bind to a portion of genomic DNA that has separated into two strands. The labeled probe binds to one of the strands. However, distinguishing between homologous genes or chromosomes using standard FISH methods would be useful. Therefore, methods of distinguishing between homologous genes or chromosomes are provided.